A pipe union for interconnecting two coaxial pipe ends is often utilized to transmit fluid under pressure during oilfield service operations. Typical high-pressure operations include mud logging, cementing, fracing, acidizing, nitrogen pumping, and other upstream well servicing applications.
One such coupling apparatus for connecting two pipe ends in an oilfield flowline is a clamp-type union connection positioned at the pipe joint. A clamp surrounds the adjacent ends of the two lengths of pipe to be interconnected. The clamp is tightened around the ends of the pipe lengths by associated wing nuts and bolts, and the individual pipe sections are drawn axially toward one another, compressing a seal located in between to complete the joint. Clamp-type couplings, however, take considerable time to install and replace, and are therefore only appropriate in relatively permanent installations.
Another common apparatus for high-pressure flow transmission at a pipe joint is a threaded hammer union, which allows two coaxial threaded sections of pipe to be connected without rotating the pipe sections. Hammer unions allow pipeline couplings to be quickly and easily effected or released, and are effective under high-pressure conditions. As such, hammer unions are often used in flowline rigging when working pressure conditions can approach 15,000 psi. The nut of the hammer union is screwed onto the external thread, drawing the connecting pipe sections axially toward one another, and compressing a sealing ring to complete the proper connection.
Conventional hammer unions have been made from a wing nut, wing nut segments, male and female ends, and a segment retainer ring. One prior art hammer union, illustrated in FIG. 1, features a 90 degree angle at the contact interface between the male end 3, the wing nut segments 4, and the wing nut 5. Such known hammer unions have performed well in many applications. There are some applications, however, where the cyclic nature of the loading is so severe that fatigue failure is possible.
Another prior art hammer union, illustrated in FIG. 2, features a 45 degree shoulder at the contact interface between the male end 6, the wing nut segments 7, and the wing nut 8. Although this configuration offered better fatigue resistant properties than the 90 degree configuration, the 45 degree shoulder design introduced unwanted inward radial stresses on the male end which were not present with the 90 degree configuration.
Therefore, where cyclic loading comprises a significant part of a particular application of a hammer union, a new and improved hammer union is desirable which reduces inward radial stresses and stress concentration levels on the hammer union, thus improving performance and reliability of the hammer union component parts.